Implication of water depth on stable isotope composition and skeletal density banding patterns in a Porites lutea colony: results from a long-term translocation experiment

Abstract

This study investigates the effect of water depth on stable isotope composition and density-band formation in the skeletal material of the zooxanthellate coral Porites lutea. In February 1991, several colonies were stained with Alizarin red-S and then transferred from 6 to 40 m. Ten years later, in February 2001, one colony was retrieved and analyzed. This provided us with the unique opportunity to maintain the coral’s genetic integrity and hence to isolate environmental factors affecting skeletal isotopic composition and density patterns. Despite extreme environmental changes experienced by the corals, the downward transplants showed no mortality after 10 years. Acclimatization of the coral to the deep-water environment involved changes in mean annual extension rates and colony morphology. The growth rate at 6 m was 5.66±0.47 mm/year, almost twice the growth rate following transplantation to 40 m, which was 3.00±0.37 mm/year. A significant difference in mean annual δ18O between the shallow and deep growth phases (−3.10±0.10 and −2.80±0.14‰, respectively) and amplitude (1.14±0.15 and 1.49±0.20‰, respectively) was detected. Mean annual δ13C in the shallow growth phase was −1.58±0.12‰, significantly heavier than that of the deep growth phase which was −1.92±0.14‰. The phase relation between δ18O and δ13C was also depth dependent. These results suggest that the role of the kinetic effect in determining skeletal isotopic composition of deep-water hermatypic corals in the study site is greater than in that of shallow-water colonies. The timing of density-band formation was found to be depth independent. At both depths, low-density skeleton is produced during summer, and high-density skeleton is produced during winter, implying that it is intrinsically controlled rather than environmentally governed. The implications of these results on paleoclimate and sea level reconstruction are discussed.

Notes

Acknowledgements

We wish to thank A. Genin for the SST data. We also thank M. Ravid of the Chaim Shebe Medical Center for helping with x-radiography work and Y. Levy for image processing. A special thanks to R. Klein who initiated the translocation experiment, and to the Marine Laboratory at Eilat for the warm hospitality. We would also like to thank A.G. Grottoli, A. Juillet-Leclerc, and T.A. McConnaughey for their constructive comments on the manuscript. This work was supported by Raynor Chair for Environmental Conservation Research to Y.L.